1. Field of the Invention
The present invention concerns a system for communicating data and control signals between a master station and plural satellite stations which may have a slave relation to said master station.
Conventionally, a transmission network may be organized to operate in a loop mode for transmitting information in serial data format between the master and one or more satellite stations.
2. Description of the Prior Art
FIG. 4 illustrates the configuration of a conventional loop mode transmission system comprising a plurality of stations 1 through 6. In the figure, a single master station 1 serves to monitor the system's operation and control the polling of other satellite or slave stations that also are connected in the loop. The master station 1 is connected directly to only two adjacent slave stations 2 and 6 by transmission links 7 and 12, respectively. The remaining satellite stations 3 through 5 are connected only to adjacent slave stations by transmission lines 8-11 and communicate with the master station through other slave stations in the loop. Each of satellite stations 2 through 6 has transmission equipment, including a computer and input/output devices, for receiving/transmitting data from/to the master station 1.
In an operation of the system in FIG. 4, data for one or more satellite stations in the network is addressably transmitted from the master station 1 via the transmission line 7 to satellite station 2. Station 2 selects the data addressed to it and passes on the balance of the data to satellite station 3 via the transmission line 8. Station 2 may also insert into the serial stream data addressed to the master station. In a similar fashion, each of stations 3-6 remove their addressed data and pass the remainder, including data addressed to the master station, to other stations through respective transmission circuits 9-11. The last station 6 transmits the assembled data stream via the line 12 to the master station. Thus data is transmitted in the transmission system in a loop mode.
In a loop transmission system, both data and control signals that are transmitted from the master station are regenerated, amplified and relayed to the next satellite station in the loop. Consequently, the transmission distance can be made long. Moreover, the transmission speed can be raised to a high rate. However, if an abnormality in any of the satellite stations occurs, amounting to a station breakdown, the entire system will be shut down.
FIG. 5 illustrates the configuration of a conventional, addressable data transmission system that is organized to operate in a bus mode. In the figure, the master station 13, which controls the data transmission, is connected to plural satellite stations 14-17 that are operative to receive/transmit data from/to the master station by means of input/output devices and to process data by a resident computer. A transmission trunk line 18 connects each of the satellite stations in parallel with the master station. Lines 19-22 are the branch lines that respectively connect the stations 14-17 with the trunk line. Each of the stations inputs only the transmitted data that is addressed to it.
Next, the function of the bus mode of data transmission is described in FIG. 5. As shown in the figure, data transmission from the master station 13 is transmitted through the transmission trunk line 18; the transmission is received by the satellite stations 14-17 through the branch lines 19-22 and input in the respective satellite stations.
In a transmission system operative in a bus mode, the transmission trunk line 18 is not interrupted by any of the satellite stations connected to it. Hence, the impedance of the satellite stations is set higher than that of the transmission trunk line. Thus, if an abnormality should occur within any of the satellite stations, its breakdown will not affect the other stations. The master station can continue to transmit data and communicate with the satellite stations other than the one affected by the breakdown. However, unlike the loop mode, because this mode does not employ the regenerative relay method, its transmission distance and transmission speed is limited.
It is an object of the present invention to overcome the problems that occur in the conventional transmission system operating in a loop mode when an abnormality occurs in any single satellite station in the loop, such that the operation of the entire system breakdowns.
It is a further object of the present invention to identify a station in which the abnormality occurs.
It is yet another object of the present invention to avoid any significant delay after a station breakdown before system operation can be restored.
Finally, it is an object of the present invention to provide a network design that is well suited for long-distance, high-speed transmission.
In particular, the present invention is designed to resolve the problems in the conventional loop mode and bus mode systems while being capable of transmitting data at a relatively high speed. The system is designed so that even if abnormalities occur in a number of satellite stations, the system will not breakdown and can continue to transmit data.